Synchronous driving system



June 16, 1931. A. M. CUR-ns' SYNCHRONOUS DRIVING SYSTEM Filed Dec.

@jy/M Arron/ver Patented June 16, 1931 UNrri-:DN STATES PATENT OFFICE`USTEN M. CURTIS, 0F EAST ORANGE, NEW JERSEY, ASSIGNOR T0 BELL TELEPHONELABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEWYORK SYNCHRONOUS DRIVING SYSTEM Application led December 2, 1927. SerialNo. 237,346.

. This invention relates to synchronous telegraphy and an object is toincrease the reliability and eiiiciency and reducel the maintenanceexpense of constant speed synchronous driving systems that utilize avacuum tube oscillator as the source of constantfrequency current. y

In high speed synchronous communication systems vacuum tube regenerativetuning 1o forks are sometimes used as sources of constant frequencywaves.` These Waves are applied to a polar relay which vibrates insynchonism therewith and supplies from its contacts positive andnegative current alternately to the primary winding of a transformer,

the secondary ofy which is connected to the armature of a synchronousmotor. In normal operation vacuum tube oscillators of the type utilizedproduce a distorted wave due to the presence of even harmonics. Theeffect of such a distorted wave on the relay is to cause it to remain inone position longer than in the other and to feed an unbalanced cur- Yrent to the transformer. This unbalanced current may be resolved into adesired a1- ternating component and an undesired direct currentcomponent which reduces the effective permeability of the transformercore material and causes the transformer to draw an excessivemagnetizing current from the relay. This heavy current burns'the relaycontacts which as a result require frequent attention. Applicant hasdiscovered that by placing a low pass filter in the output circuit ofthe vacuum tube to remove the even harmonies from the wave supplied andthus prevent biased operation of the relay, the'transformer magnetizingcurrent is materially reduced and as a result'burning of the relaycontacts is to a large extent avoided.

'In the drawings, Fig. 1 disclosesa fork controlled vacuum tubeoscillator containing a ilter in accordance with this invention; Figs. 2and 3 are curves representing the output wave of such an oscillatorwithout and with the filter respectively; and Fig. 4 shows amodification of Fig. 1 wherein lilters are employed in each circuitconnecting the frequency setting fork system with a device to becontrolled. y

Referring to Fig. 1, the apparatus Within the rectangle represents acomplete fork controlled vacuum tube oscillator adapted to supplyalternating current of constant frequency to two independent circuitsthrough the output transformers 14 and 15. A relay driving a synchronousmotor through a transformer is shown connected to transformer 15 and asimilar` apparatus may be operated fromr and 15. The oscillator isadapted to draw L energy for both the filament and plate circuits of thevacuum tubes from a single source 28. Resistances 23, 24 and 2l areconnected in series with the filaments of the tubes to reduce thevoltage to the proper value. The fila-ments of all the tubes areconnected in series and the proper grid-biasing voltage for each tube isobtained by connecting its grid ret-urn lead to such a point in thefilament circuit as to utilize the voltage drop in the resist-ances 23,and 24 and the filaments of some of the other tubes.

The resistances 22, 25 and 26 reduce the voltage of power source 28 tothe proper values for application to the plates of the different tubesand alsoA serve as protection devices to limit the current iiow in caseof a short circuit in the wiring.

Electromagnet 2 mounted at the end of fork l and energizedthroughresistances 20 .from source 28 is to compensate for the effect onthe fork frequency of variations in the voltage of the power supply.Thus if the voltage of source 28 should increase, it would increase thespace current of tube 5 and deliver more power to the polarizedelectro-magnet 3, which would tend to increase the magnitude ofvibration of the fork. The increase in voltage of source 28 would,however, also increase the magnetic attraction of electro-l magnet Q outhe fork tines. This has the etllect ot increasiire` the tension in theforli tines and also of increasing the Work done by the tincs iu cuttingthrough the magnetic field of the electromaguet. lioth efiects tend toreduce the aiu plitudc oit vibration and couipensate i'or the strongerdriving impulz-scs from magnet 3.

lt is to bc understood that an increase in the amplitude oi'l vibrationreduces the 'lirequcncy, and yicc Vversa. ller this reason \'a riableresistance 27 is inserted in the drive magnet circuit 'to malte fineiuljustments in 'frequency by varying the amplitude.

In oiniration.l the motion oit the steel Jforli tiues changes the thu;in the polarized pichup coil 1, which has a permanent magnet core, anddevelops an elcctron'iotive torce corresponding in frequency to thefrequency et vibration oi" the forli. rl"his electromotivc torce. isapplied to the grid oit oscillator tube 5 and the amplified energy Yfromthe output oit thc tube is ted baci: through the seconda ry Winding S ottransformer G, condenser 29 and variable resistance QT to drive .magnet3, which also is permanently polarized by suitable means. When `thcspaces l'ietwc. the pick-i p and drive magnoten and the toi-li tines,are adjusted 'for stable operation, it is founfl that theI amplitude oitviln'a'timi is limited by the oscillator tube 5 which overloads and actsto limit the amount et power applied to tram-:former t and the drivemagnet The Wave supplied by tube 5. when the tube is overloaded, isbadly distorted, due to the presence chiefly of even harmonics, and mayhave. a form like that oit the curve in Fig. 2. lit such a Ware wereapplied to polar relay 1G, it would cause the a rniature of the `rel ayto lie against one coutact longer than the other. That this is the ascmay readily be seen from a study oit Fig. Q in which lines 31 and 5:32above and below the Zero line respectively, indicate the potentialrequired to operate relay 16. Thus at time A the relay would operate toclose on one contact and remain in that position until time l when itwould operate to close on the other contact. The average lengths ot timeduring which current l'iows in each direction through the primaryVWinding of transformer 18 are theretore proportioiuil to the distancesAll) and BU. lfhe nct result ot applying current to the transita-mer torlonger periods .in one direction than in the other is to produce anunbalanced direct current in one direction which tends to saturate thecore material. As a direct result ot this saturation, the permeabilit?,7of the transiormer core material is reduced; the inductance ci theprimary Winding is reduced, and an increased magnetizing current isdrawn from battery 17 over the contacts ot relay 16. The increasedcurrent may cause the contacts to corrode much more rapidly than theywould if the core were not saturated.

The distortion in the oscillator output Wave may be reduced to a certainextent by increasing resistance 27 so that the amplitude ot vibration ofthe Yfork is imaiilicient to overload tube 5, but under such conditionsthe 'fork is unstable and the output power is greatly reduced.Accordingly, it is ttouud preferable to permit the oscillator tube towork overloaded and to inscriJ a low pass filter l() oit conventionaltype in the output circuit. This filter is designed to cut olin Waveso't frequencies slightly higher than any 'frequency at which theoscillator would normally operate, but to permitthe fundamental Waye topass With little attenuation. The cut-ofi point ot the lilter Will stillbe louT enough, however, to greatly attenuate all harmonics so that theWave applied to the transformer 11 may be practically a pure sine Wareas I shown in Fig. 3. It may readily be seen that the relay 1G whenoperated by a pure Ware such as that shown in Fig. 3 Would always beheld for the same length of time in each position, and that,accordingly;there would be no average unidirectional magnetizing currentin transformer 18 to produce saturation and the resultant contacttrouble as outlined above.

Although in Fig. 1 the filter 10 has been i inserted between theoscillator tube and the amplifier tubes 12 and 13, two filters 10 may beused as shown in Fig. l, one inserted in eachof the output circuits oiamplifier tubes 12 aud 13. `Where tubes 12 and 13 are overloaded so asto introduce considerable distortion themselves, it would beadvantageous to insert the filter in the amplifier output circuits.

lVhat is claimed is:

1. A synchronous driving means comprising a source o't `alternatingcurrent waves ot unsymmctrical torni, a relay operated by said Waves tosupply current pulses ot alternately opposite polarity over itscontacts, an inductive circuit which comprises a magnetic core ot'material the permeability o'i which decreases athigh'magnctizing forces,for producing in response to said pulses ot alternately oppositepolarity au altrnating current wave of a. uniform maximum amplitude, anda selective circuit inserted in said source of unsymmetrical Waves torender said Waves symmetrical. in form.

2. A synchronous driving means compris- `ing a source of alternatingcurrent Wares of nnsymmetrical i-orm, a relay operated by said Waves tosupply current pulses ot alternately opposite polarity over itscontacts, au inductive circuit comprising a transformer having a coroolinaterial the pernuaibility o t which decreases at high magnetizi ngforces, ,vor producing in response to said pulses oil" alternatelyopposite polarity an alternating current Wave of a uniform maximumamplitude,

and a filter circuit inserted in said source of unsymmetrical Waves torender said waves symmetrical in form.

3. A self-oscillatory circuit for driving a relay at a constant speedand in an unbiased manner comprising a vibratory mechanical element, apick-up coil for deriving energ from said element, circuit arrangementsfor feeding back energy from said coil to said element to maintain'it invibration comprising a discharge device amplifier and a drive coil, anda circuit connecting said pick-up coil withsaid relay through saidamplifier including a filter between the amplifier and the coil forsuppressing harmonics of the frequency of said element.

4. A source of waves of unsymmetrical form, a relay operated by Wavesfrom said source and having contacts associated with a source of directcurrent, an inductive circuit comprising a magnetic core arranged tocontrol the output current intensity to be supplied with current pulsesof alternately opposite polarity from said source of current by saidrelay, and a selective circuit inserted between said source of waves andsaid relay whereby said Waves are made symmetrical.

5. A source of waves of unsymmetrical form, a `polar relay operated bywaves from said source-and having contacts associated with a source ofdirect current, an inductive circuit which ycomprises a magnetic core ofmaterial the permeability of which decreases at high magnetizing forces, supplied with current pulses of alternately opposite polarityfrom said source of direct current by said polar relay, and a low passfilter inserted between said source of waves and said relay whereby saidwaves are madesymmetrical.

6. A source of waves of unsymmetrical form, a polar relay operated byWavesfrom said source and having contactsv associatedv with a source ofdirect current, a transformer circuit comprising a core of material thepermeability of which decreases at high magnetizing forces, suppliedwith current pulses of alternately opposite polarity from said source ofdirect current by said polar relay, and a low pass filter insertedbetween said source of waves and said relay whereby said waves are mademore symmetrical.

7 A source of waves of unsymmetrical form comprising a vacuum tubeoscillator the fundamental frequency of which ma be adjusted between setlimits, a low pass lter connected to said source having a cut-off pointhigher than the upper frequency limit of said source but lower thantwice the lower limiting frequency of said source, a vacuum tubeamplifier for amplified waves received from said filter, a polar relayoperated by the amplified waves having an armature movable between twofixed contacts, a transformer havlng a primary winding with a mid-tap,

the ends of said primary winding being connected to said respectivefixed contacts of said relay, a source of direct current connectedbetween the mid-tap and said armature, a secondary winding on saidtransformer, and a synchronous motor connected thereto.

8. In combination, a source of electric oscillations comprising athermionic vacuum tube having an input circuit and an output circuit, avibratory element, magnetic driving means controlled from the outputcircuit of said tube for vibrating said element, means responsive to themotion of said element to produce an electromotive force connected totheinput of said tube, a low pass filter connected to the output circuitof said tube, a polar relay operated by waves received from said tubethrough said filter and having a contact movable between two fixedcontacts in response to said waves, and an inductive circuit suppliedwith current flowing in one direction therethrough from the movablecontact when it is in one position and in the opposite direction whenthe movable contact is in its opposite position.

9. A source of constant frequency alternating current, a filterconnected thereto for removing even harmonics from the wave produced bysaid source, a plurality of vacuum tube amplifiers, the input circuitsof which are connected to the output circuit of said filter, a relayconnected to the output circuit of each amplifier, an inductive devicehaving a core subject to magnetic saturation, a source of directcurrent, contacts on said relay, and connecting means between saidcontacts, said source and said inductive means whereby said relay invibration supplies current pulses of alternately opposite polarity fromsaid source of current to said inductive means.

In witness whereof, I hereunto subscribe my7name this 30th day ofNovember, A. D. 192

AUSTEN M. CURTIS.

